In many electronic systems there is a need to interconnect high-performance parallel buses or assemblies. A parallel computing system having a plurality of processors, where processors are located on separate circuit assemblies, is an example of this need. The circuit assemblies may be in the same cabinet or in different cabinets. In either case, the assemblies may not be precisely located with respect to each other.
Assemblies may be displaced with respect to each other in a variety of ways. One type of displacement is where the assemblies are parallel, but are not coplanar. A second type of displacement is where the assemblies are not parallel. A third type of displacement is a variation in distance between the assemblies. A fourth type of displacement is a lateral misalignment between the assemblies.
Presently, parallel cables are being used to interconnect such circuit assemblies. Their flexibility accommodates a limited amount of non-coplanarity, nonparallel variations, displacement variations, and transverse misalignment.
A prior art parallel cable is shown in FIG. 1. The cable uses a four-layer flexible circuit board ("flex circuit") as its major component to transmit electrical signals between respective pins of its two connectors. The flex circuit's inner two layers have conductive traces that transmit electrical signals. Its outer two layers are solid copper ground planes that provide current return paths and constant impedance for the signal traces. The cable's flex circuit portion can be bent into a "U" or "S" shape so that its connectors are properly positioned for mating connectors on two circuit assemblies to be interconnected.
The cable shown in FIG. 1 has a variety of disadvantages. The cable is fairly stiff, preventing its connectors from being easily mated and unmated with mating connectors one at a time. If the cable connects circuit assemblies in different cabinets, mating and unmating the connectors can be especially inconvenient. Furthermore, if the mating connectors on the two circuit assemblies to be interconnected are not coplanar, the cable and its connectors are under continual stress. The cable is fairly tall, and not in the plane of the circuit assemblies it interconnects. Therefore, it requires a relatively large cabinet to contain it. The cable also is likely to block cooling airflow.
When the cable is configured to provide a "service loop" and positioned for mating it must be formed into a "U" shape which makes its length relatively long for the distance it spans. As crosstalk and electrical interference are proportional to a cable's length, a shorter cable is preferred.
What is desired is a parallel transmission cable which is relatively flexible, allowing its connectors to be independently mated and unmated, which is relatively short for the distance it spans, which accommodates variation in displacement between mating connectors, and which is relatively compact to allow increased cooling airflow and decreased size requirements, yet maintains controlled electrical transmission characteristics.